The invention relates to a cassette tape recorder, and more particularly to a cassette tape recorder for use with a tape cassette which internally houses a length of a magnetic tape having its opposite ends secured to a pair of tape hubs rotatably disposed within the cassette. In particular, the invention relates to a miniature cassette tape recorder for use with a micro-cassette tape of a size which is comparable to a packet of matches.
In the operation of tape recorders, it is desirable to stop the operation of the recorder automatically when a tape end is reached, by detecting this condition by some means. A variety of techniques have been heretofore proposed to achieve this end. Specifically, a conductive foil is applied to the terminal end of a magnetic tape so that it can be electrically detected to activate a stop device. Alternatively, a terminal end of the tape may be provided with a portion having a different optical reflectivity or transmittivity from that of the magnetically active surface so that the portion can be optically detected to activate the stop device. In a further alternative, the tape tension applied to a guide roller by the magnetic tape is utilized by mechanically detecting a change in the tension when the tape end is reached, thus activating the stop device.
However, it is extremely difficult and expensive to work the terminal end of a tape which is contained in a tape cassette in order to make it capable of cooperating with the tape recorder. For this reason, mechanical stop means which utilizes the tape tension, sometimes referred to as a mechanical stop, will be advantageous. The cassette tape has its one end secured to one tape hub and the other end to the other tape hub, both contained in the cassette, so that the rotation of tape hub will be interrupted when a tape end is reached. As a result, the tape driving shaft which engages the tape hub will slip relative to the tape hub, resulting in an increased load. Thus, a increase in the load may be detected to activate the mechanical stop.
However, in order to assure an accurate detection of a change in the load of the tape driving shaft, the mechanical stop device will be extremely complex and bulky. While such device may be incorporated into a conventional tape recorder which is used with a conventional tape cassette of a standard size, which is known as a compact cassette, there is no space available for the provision of such device in a miniature tape recorder as contemplated in the present invention, which is of a size such that the entire tape recorder can be received in the pocket of a suit or shirt.
In either micro-cassettes or compact cassettes, the tape hubs on which the magnetic tape is disposed and secured have a certain degree of freedom to be displaced or rattled relative to the cassette in order to facilitate the fitting engagement of the tape hubs on the tape driving shafts when the tape cassette is loaded on a tape recorder. In accordance with the invention, the operation of the tape recorder is automatically stopped when a tape end is reached, by detecting a shift of a tape driving shaft associated with the tape supply hub, as permitted within the tolerance of the clearance between the tape hub and tape driving shaft, which occurs as a result of the tape exerting a drive on the tape supply hub to which its terminal end is secured, and hence on the tape driving shaft also which is associated therewith when the tape end is reached.
Usually, a recording operation of the tape recorder is established by depressing both a record and a playback button to their operative positions where they are maintained. It will be convenient if it is possible to detect, when depressing the record button, whether or not the cassette loaded retains the lug which is usually provided for preventing an inadvertent erasure of a recorded tape.
A conventional tape recorder is designed to permit a rapid advance, rewind, queing or review operation of the tape, in addition to the recording, playback and stop operations. However, in a conventional tape recorder, each of the first mentioned operations is only enabled when its devoted button is depressed, thus resulting in an increase in the number of operating buttons and the space requirement therefor. This presents a serious limitation on the design of a miniature tape recorder which is adapted for use with a micro-cassette. In accordance with the invention, the rapid advance, rewind, queing and review operations are enabled by a single button which is operated in different directions.
Usually, the tape rewind operation is performed by depressing a rewind button. The rewind button may be held depressed manually or locked in the depressed position. For the purpose of the invention, it is preferable to lock the rewind button in the depressed position. The rewind button is reset from the depressed position upon depression of another button, thus simplifying the overall arrangement.
The capstan of the tape recorder is usually provided with an integral flywheel in order to provide a stable rotation of the capstan, and the drive to the capstan is transmitted through the flywheel. In an attempt to provide a compact structure, some tape recorders are constructed without a separate thrust bearing for the capstan shaft. To dispense with it, the flywheel and its drive wheel are disposed at right angles to each other so that the drive wheel bears against the end face or the peripheral edge of the flywheel. As a result, the capstan and a motor must be arranged such that the capstan shaft and the motor shaft are disposed at right angles to each other. However, with the recent development of a flat miniature motor, it is necessary that the capstan be disposed in alignment with the motor shaft. In this instance, the drive wheel will have to bear against the peripheral surface of the flywheel, so that the drive wheel cannot provide a thrust bearing for the capstan.
During a recording or playback operation, the capstan is driven by the motor so that it cooperates with an oppositely located pinch roller to feed a magnetic tape disposed therebetween at a uniform speed. Usually, an idler or an idle roller is disposed between the output shaft of the motor and the flywheel associated with the capstan so as to transmit the drive to the flywheel through the idler. As the overall size of the tape recorder is reduced, the moment of inertia of the motor rotor, capstan and flywheel has a relatively significant influence upon the overall drive system. In particular, with a portable tape recorder, the angular velocity of the rotor and the flywheel will change as an external force is applied as by swinging the tape recorder, and unless such force is compensated for by some means, there results a non-uniformity in the rotation, giving rise to wow or flutter. However, in the conventional arrangement in which the idler is simply located between the output shaft and the flywheel, the rotor of the motor and the flywheel associated with the capstan rotate in the same direction to produce a synergetic effect in terms of the moment of inertia of the rotor and the flywheel, which when combined with an external force, cannot be balanced by the idler alone, thus again resulting in a non-uniformity in the rotation.
The idler which is used to transmit the drive from the motor to the capstan may comprise either a roller or a pulley, either of which is mounted on a rockable support plate so as to be moved into or out of engagement with the flywheel. One of the problems associated wth the idler is the fact that the support plate for the idler occupies a relatively large space within the tape recorder, thus standing in the way of miniaturization of the tape recorder.
If the idler is mounted on a rockable lever, the limited freedom of movement of the rockable lever which results from its pivotal mounting requires a precise adjustment in the location of the rockable lever so that it bears against both the drive wheel and the flywheel with an equal pressure. However, because the available space is limited, it is extremely difficult to provide a sufficiently precise adjustment, usually resulting in a compromise. However, when such an arrangement is employed in a portable or pocket type tape recorder, oscillations may be caused to the rockable lever when the recorder is swung to cause an unbalance in the pressure with which the idler bears against the drive wheel and the flywheel, thus tending to cause a non-uniformity in the rotation of the capstan.
To provide an effective transmission of the drive from the motor to the capstan through the idler, it is necessary that the peripheral surfaces of the idler, the output wheel and the flywheel associated with the capstan be maintained in proper abutting relationship. However, the drive wheel and the flywheel are frequently skewed to a degree depending on the manner of mounting the motor or the capstan. In particular, the motor is mounted with an interposed vibration absorbing resilient member, so that the drive wheel tends to be skewed more strongly to cause an unbalanced bearing or abutting relationship between these members, resulting in a varying axial force applied to the idler. This tends to cause non-uniform rotation, which gives rise to wow or flutter or increases the load and hence the power dissipation of the motor.
It is also known to provide a cassette tape recorder which may be connected with an electroacoustic instrument such as a radio set or stereophonic player so that a recording or playback operation can be performed in combination therewith. The tape recorder itself is usually provided with an auto stop mechanism which automatically interrupts the operation of the tape recorder when the tape running is terminated. One of the problems which arises when such tape recorders are combined with the electroacoustic instrument is that while the operation of the tape recorder may be interrupted by the auto stop mechanism, the electroacoustic instrument which is coupled with the recorder remains in operative condition, resulting in a waste of the electric power.